1. Field of the Invention
The instant invention relates to a threaded fitting and ferrule for installing in a profiled through-hole of a bulkhead or the like, which, when inserting a cable (or wire) therethrough and threading the fitting into the bulkhead sequentially provides for both a water tight seal and a strain relief.
2. Prior Art
It is a common problem when an electrical connection must be subject to withstanding outdoor usage, as the climate (particularly rain and moisture) can degrade an electrical connection to the point of allowing no current flow. Typically in such a situation, a cable having insulation therearound will provide the conductor with ample protection. The conductor must, however, be terminated at some point to an electrical connector, and the electrical connector will most likely be enclosed in a sealed junction box. In order to protect the electrical interconnection inside the sealed junction box, the entry for the cable into the junction box must also be sealed. Typically, a fitting of some sort is provided having an opening passing through the fitting for the cable to pass through and a threaded portion for connection to the box. Most of the sealed fittings heretofore have utilized a gasket, O-ring or the like which too often are subject to degradation from adverse weather.
U.S. Pat. No. 3,567,843, for example, discloses such a connector. This fitting includes an externally theaded nut and an internally threaded and mating body, the body portion having a ramped or cam surface on the inner diameter. Disposed between the nut and body is a grommet having a ramped surface matching the ramp on the body portion, such that when the body and nut are threaded together, the body portion wedges the grommet radially inwardly towards the cable.
U.S. Pat. No. 4,273,405 also discloses a sealed fitting having an internally threaded member and a mating and externally threaded nut. Once again, a sealing ring and a retaining ring are installed, each of which is subject to weather degradation. Furthermore, the number of components required to complete the seal relates to the purchase price of the fitting and also to the ease of field installation and/or repair.
Another fitting is known which utilizes a collet having threads therearound for mating with a domed sealing nut. Installed in the collet is a sealing ring, which, when the nut and collet are threaded together, compresses radially inwardly due to the radial inward movement of the collet.
In addition, when the fitting is being tightened, as for example, when a threaded fitting is being screwed into an internally-threaded opening in a wall or bulkhead of a junction box, there is no convenient means to determine if the proper torque on the fitting has been reached and, therefore, no convenient means to determine if the cable within the fitting could withstand at least a desired minimum axial pull-out force for a proper strain relief. The use of special torque-releasing wrenches to be applied to the fitting is generally impractical, besides being time consuming, especially since the installation personnel may be semi-skilled and are often required to perform their work under difficult conditions.
Accordingly, it would be desirable to assure a proper strain relief as well as a water-tight seal for the cable. More specifically, it would be desirable to guarantee that the cable is retained in the bulkhead to meet a desired minimum axial pull-out force on the cable. For example, for underground feeder ("U.F.") cables used in the solar industry, it is necessary to assure a minimum of a twenty pound pull-out force on the cable in order to meet Underwriters Laboratory ("U.L.") specifications.